Troubleshooting Inverter Overcurrent (oC) Alarm on Yaskawa A1000 & GA700 Drives
1. Overcurrent Detection Architecture in Yaskawa Drives
On Yaskawa A1000, V1000, and GA700 series AC drives, the oC (Overcurrent) alarm represents the highest-priority hardware protection routine engineered to preserve the IGBT (Insulated Gate Bipolar Transistor) power modules. Hall-effect current transducers on output terminals U, V, and W sample instantaneous phase current vectors at microsecond intervals. If instantaneous output current surpasses 200% to 220% of rated drive current, internal gate drive protection shuts down firing pulses within microseconds to suppress destructive thermal runaway across the silicon junction.
2. Operational Fault Timing & Diagnostic Matrix
| Trip Timing Event | High-Probability Root Cause | Technical Verification Test | Engineering Corrective Action |
|---|---|---|---|
| Trips instantly at power-up (Before Run command) | Shorted / punctured IGBT power transistor | Perform static diode junction test from U, V, W to DC Link | Replace IGBT power bridge and inspect gate drive optocouplers |
| Trips during initial acceleration (During Accel) | Acceleration rate too steep or mechanical rotor lock | Disconnect motor cables and run drive unloaded to isolate load | Extend Acceleration Time (Parameter C1-01) or attenuate torque boost |
| Trips at steady commanded speed (During Run) | Sudden mechanical load surge or intermittent motor phase ground fault | Megger motor insulation resistance at 500VDC | Inspect machine bearings and inspect motor leads inside flex conduits |
| Trips during deceleration ramp (During Decel) | Deceleration ramp too aggressive causing regenerative overcurrent | Monitor DC bus voltage rise during deceleration | Lengthen Deceleration Time (C1-02) or integrate dynamic braking unit |
3. Static IGBT Power Module Diode Verification Protocol
- Lock Out Main Power: Disconnect incoming 3-phase mains. Wait until the red 'CHARGE' LED has extinguished and measure DC bus voltage across `+1` (or `+2`) and `-` to confirm residual voltage drops below 5VDC.
- Isolate Motor Terminals: Disconnect motor leads U, V, W completely from drive output terminals.
- Configure Multimeter to Diode Test:
- Test Upper Arm Transistors: Place negative (black) meter lead on DC bus positive terminal `+1` (or `+2`). Probe terminals `U`, `V`, and `W` with positive (red) lead. Balanced forward bias drops of 0.30V to 0.48V must be measured across all 3 phases. Reversing probe polarity must show OL (Open).
- Test Lower Arm Transistors: Place positive (red) meter lead on DC bus negative terminal `-`. Probe terminals `U`, `V`, and `W` with negative (black) lead. Expect matching forward readings (0.30V - 0.48V); reversed polarity must read OL.
- Evaluate Silicon Health: Any phase indicating 0.00V or generating an audible continuity tone confirms a permanently shorted IGBT module requiring professional repair.
4. Tuning Stall Prevention on Yaskawa A1000 Drives
When hardware testing confirms IGBT integrity but overcurrent trips occur under heavy rotational inertia (heavy centrifuges, industrial blowers, indexing tables), tune Stall Prevention parameters to allow dynamic current throttling: - C1-01 (Acceleration Time 1): Increase acceleration duration from 5s to 12-15s. - L3-01 (Stall Prevention Selection during Accel): Set to '1' (General Purpose) to pause speed ramp increments when current approaches limits. - L3-02 (Stall Prevention Level during Accel): Set threshold to 150% to clamp output frequency until motor back-EMF stabilizes.